1. Field of the Invention
The present invention relates to an image processing apparatus which processes time-series images obtained through image pickup along time series by an imaging device and an image processing method thereof.
2. Description of the Related Art
In recent years, in a field of endoscope, a swallowable capsule endoscope is proposed. The capsule endoscope has an imaging function for picking up (or taking) images inside a subject, a transmission function for radio transmitting image information obtained through image pickup by an imaging unit, and the like, and is configured with a capsule-like casing housing these functions. For the introduction of the capsule endoscope into a subject, a patient, i.e., the subject of an examination swallows the capsule endoscope from the mouth. The capsule endoscope travels through inside the subject body, e.g., through internal organs such as an esophagus, a stomach, a small intestine, and a large intestine following peristaltic movements thereof until naturally excreted from the body. While moving through inside the body, the capsule endoscope sequentially picks up images of the interior of the body at the rate of 2 to 4 frames/sec, for example, and radio transmits image information obtained through image pickup to a receiver outside the body. Images of the interior of the subject picked up by the capsule endoscope and received by the receiver outside the body are sequentially displayed on a diagnosis-dedicated workstation or the like in an order of time series, and checked by an observer such as a doctor.
The capsule endoscope picks up an enormous amount of images. Hence, the diagnosis-dedicated workstation or the like determines whether each image is worth observation or not based on a degree of similarity between adjacent images in time series. Then, the workstation or the like adjusts display time of each image by lengthening the display time of an image which is worth observation, and shortening the display time of an image which is not worth observation, so as to alleviate the burden of image observation on the observer. As one technique for the above, it is known to set plural pixel regions in an image, find a motion vector of each pixel region between images successive in time series, and determine a degree of similarly of the images. For example, according to one known technique, a motion vector of each pixel region is calculated with respect to successive images in time series; a motion vector with a largest motion vector amount (or length) is selected; and a display time of each image is calculated based on the motion vector amount (representative motion vector amount) of the selected motion vector. Further, according to another known technique, an image which shows an identical imaging scene with other image is found by checking whether each of calculated motion vectors are in the same direction or not, and an image which shows an identical imaging scene with other image which is adjacent thereto in time series is displayed for a short time period or is skipped (see Japanese Patent Application Laid-Open No. 2006-280792).